| China is a large agricultural nation, agricultural water demand is bigger. But for a long time, per capita water is relatively scarce in our country, especially in recent years, the problem of drought, soil and water loss,soil desertification and so on is becoming more and more prominent, at the same time, the rainfall (rewater) after irrigation and nitrogenous fertilization is prone to cause the leaching of nitrogen and deep seepage in the soil, it not only will cause the utilization rate of nitrogen decreased, but also cause groundwater pollution and bring about serious influence to recycling of water resources and agricultural, industrial and domestic water, Therefore, seeking a way of water-saving protecting fertilizer and development methods of water use is more urgent and important. In view of the above situation, professor Sun put forward a new water saving irrigation methods for fruit forest in hilly area———Water storage pit irrigation. This method is a new irrigation method which combines water saving-irrigation and soil conservation. It can meet the water saving and drought resistance requirements, and can make full use of local rainfall runoff to control soil erosion. After years of research in water, evaporation and nitrogen migration, this method has made great progress and countless rich fruits, but the research about rewater is still in its beginning stage. Therefore, it is of great significance to study on the effect of rewater to water and nitrogen transport in soil could bring important significance for further development of water storage pit irrigation.Combined with the national natural science funds projects (50979065), the paper conducted chamber model test aiming at the effect of rewater to water and nitrogen migration in soil under the condition of single water storage pit irrigation. The effect of rewater to water and nitrogen migration in soil under different rewater volume (1.75L,3.5,5.25L) and different rewater time (1d,3d,5d,7d,10d) has been studied. By using soil water dynamics theory and soil solute transport theory in the numerical simulation established single pit soil water nitrogen mathematical model after rewater conditions, through the finite difference method and Gauess-Seidel iterative method to its numerical solution. The study result indicates that:(1) Under the condition of single water storage pit irrigation, different rewater conditions(rewater volume and rewater time) on the influence of soil moisture content mainly includes:①Because the water storage pit bottom has impervious flap, the water movement mainly is level infiltration after rewater. The overall moisture content increased, wet expanded, soil moisture in the single water storage pit decreases gradually as the radial distance increases. It firstly increases and then decreases as the vertical distance increases;②Under the same condition of rewater time, the rewater volume is larger, the larger the range migration of water, the greater the moisture content; the rewater interval time is shorter, the larger the range migration of water, water in wet body more evenly distributed.(2) Under the condition of single water storage pit irrigation, different rewater conditions(rewater volume and rewater time) on the influence of soil nitrate nitrogen mainly includes:①In the radial aspects, soil nitrate nitrogen in the single water storage pit decreases gradually as the radial distance increases. But in radial wet body edge, nitrate nitrogen reach peak and is higher than the peak rewater before. Under the same condition of rewater interval time, the rewater volume is larger, the peak of nitrate nitrogen is forward of the far, the smaller the nitrate nitrogen of the Wet body internal. Under the same condition of rewater volume, the rewater interval time is longer, the smaller the nitrate nitrogen of the Wet body internal;②In the vertical aspects, the soil nitrate nitrogen firstly increases and then decreases as the vertical distance increases after rewater, in vertical wet body edge nitrate nitrogen reach peak. Under the same condition of rewater time, the rewater volume is larger, the larger the nitrate nitrogen in vertical wet body edge.Under the same condition of rewater volume, the rewater interval time is longer, the larger the nitrate nitrogen in vertical wet body edge;③Therefore, nitrate nitrogen movement mainly is priority to with convection, a majority of nitrate nitrogen focus on wet body edge. (3) The soil in ammonium nitrogen are affected by soil particle adsorption effect. Its migration regularity is different from nitrate nitrogen:①In the radial aspects, the soil ammonium nitrogen firstly increases and then decreases as the radial distance increases after rewater, under the same condition of rewater interval time, the rewater volume is larger, the peak of ammonium nitrogen is forward of the far. Under the same condition of rewater volume, the rewater interval time is longer, the more obvious influence for ammonium nitrogen movement. But the rewater interval time being greater than5days, it is no significant effect for ammonium nitrogen movement;②In the vertical aspects, under the same condition of rewater interval time, the rewater volume is larger, the rewater volume is larger, the smaller the ammonium nitrogen;(3)The distribution of ammonium nitrogen can be seen ammonium nitrogen movement is priority to with diffuse, a majority of ammonium nitrogen focus on wet body inside.(4) This paper established single pit soil water nitrogen mathematical model, and by using the finite difference method and Gauess-Seidel iterative method solve its numerical solution. By comparing the simulation value and test data showed that both a good coincidence. So the model can be used to simulate water and nitrogen transport characteristics after rewater. |
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